This invention relates to ultrasonic flow meters and more particularly to an improved ultrasonic flow meter using a single transducer which is sensitive, accurate and simple in design.
Acoustic or ultrasonic flow meters are known and in use. These prior designs, however, are all exceedingly complex in both the design of the flow chamber and transducers and in the circuitry associated with the same. The patent to Pederson et al U.S. Pat. No. 4,011,755 dated Mar. 15, 1977 and entitled ACOUSTIC FLOW METER is one of such type. It utilizes a pair of transducers at opposite points in the flow meter between which gated bursts of relatively high frequency of acoustic energy is transmitted. The transmission is alternately in an upstream and downstream direction. By measuring the relative phase shifts of the upstream and downstream transmissions, a measurement proportional to a flow rate is obtained. The patent to E. Hausler U.S. Pat. No. 4,011,753 dated Mar. 15, 1977, and entitled METHOD AND DEVICE FOR MEASURING THE FLOW VELOCITY OF MEDIA BY MEANS OF ELECTROSOUND discloses an arrangement in which ultrasonic transducers are located at the opposite ends of a measuring section with the transducers having concave surfaces which face each other and which are located in mutual co-focal relationship. The ultrasonic transducers operate alternately as emitters or receivers or two transducers may be used at each end of the measuring section, one being an emitter and one being the receiver. By measuring transit time of the ultrasonic energy in the flow direction and in the opposite direction, a time differential proportional to flow rate is obtained.
Still other known flow meters have utilized the transducer arrangement of two emitter receiver units transmitting in both directions with a resolution of the frequency difference in the transmissions to determine time of transmission and hence, rate of flow of the medium.
A further known ultrasonic flow meter is based on the Doppler-frequency shift of a movable reflector or reflector material. The reflected sound waves are picked up by a receiver and the determined Doppler shift is used for determining the velocity of flow of the fluid. The disadvantage of this measuring method is in the extensive equipment for beaming the sound waves as well as for the elimination of temperature influence and presence of particles in the fluid necessary for the reflection of sound waves.
Another known ultrasonic device for acoustic flow measurements in fluids uses special modulation means for measuring the transit time for the sound waves along at least one path extending through the fluid. The signal generator emits an oscillation which is frequency-modulated in accord with an exacting predetermined principal and has a constant duration. The difference in transit times of the sound waves in the media is measured and the output signal representing this difference is measured by means of a timing frequency which is corrected as a function of the sound velocity of the fluid. The main drawback of this measuring device is the great band width of the acoustic electric transducer necessary for accomplishing the method.